The present invention relates to electromagnetic flowmeters and more particularly to an electromagnetic flowmeter which measures the flow of a fluid which flows through a conduit, whether or not the conduit is full of the fluid.
Conventionally, an electromagnetic flowmeter is known which measures the flow of a fluid which flows through a conduit in a state where the conduit is full of a fluid. Murase and others have proposed an electromagnetic flowmeter which is composed of an exciting coil disposed above a conduit, a pair of electrodes disposed below the conduit and circuitry which controls those coils (JP-A-01-29224). According to this flowmeter, even if the conduit is not filled with a test fluid, the measurement of the flow of the fluid is theoretically possible.
Watanabe and others have proposed a detector which detects whether a conduit is full of a flowing fluid or not, the detector comprising a pair of coils each disposed above and below a conduit, a unit for selecting and driving one of these coils, a pair of electrodes disposed on the corresponding sides of the conduit, and circuitry which selects energization of a coil, as disclosed in JP-A-59-2302115.
There are three other methods which measure the flow of a fluid which flows through a conduit in a non-full state and in a non-electromagnetic manner as follows:
1. A level measuring system which measures the level of fluid in a conduit using an ultrasonic level meter and calculates an estimated flow using formulas; PA1 2. A dam system for calculating the flow of a fluid in accordance with hydraulic formulas by measuring the level of the fluid at a dam provided intermediate a conduit through which the fluid flows; and PA1 3. A level and flow rate measuring system for calculating the flow of a fluid by measuring the level of the fluid using ultrasonic waves or pressures and measuring the flow rate in an ultrasonic or electromagnetic manner.